Co-emergence of Antiferromagnetism and Local Symmetry Breaking in the Kagome Magnet (Co_0.45Fe_0.55)Sn

Kagome-lattice materials, such as CoSn and FeSn, have attracted significant attention as hosts of electronic flat bands and topological phases. However, current understanding of their properties is primarily based on average crystal structures. Here, we report the co-emergence of antiferromagnetic (AFM) order and local symmetry breaking in nominal (Co_0.45Fe_0.55)Sn. Using a combination of neutron powder diffraction, synchrotron x-ray total scattering, and reverse Monte Carlo modeling, we uncover the concurrent magnetic ordering and local orthorhombic distortion below T_N=140 K. Despite a detectable lattice anomaly at T_N, the hexagonal P6/mmm average structure remains unchanged, underscoring a pronounced spin-lattice coupling in (Co_0.45Fe_0.55)Sn. Our findings suggest that the local symmetry breaking is strongly coupled to magnetic interactions. These results highlight the strong coupling between magnetism and local lattice distortions in kagome magnets, offering new insights into the interplay between electronic and structural degrees of freedom in these materials.